1. Field of the invention
The present invention relates to a method for the production of an air-permeable adhesive tape for medical and other applications. This type of adhesive tape also includes preparations in sheet form.
2. Description of the prior art
Adhesive plaster and other types of adhesive products employed in the medical field are directly applied to the surface of the body. The long continued application of such adhesive products to the human body prevents the dissipation of moisture from the surface of the skin, and may thereby cause skin inflammation. Therefore, adhesive products which are permeable to air are desirable, and accordingly the following techniques have previously been proposed for the purpose of manufacturing air-permeable adhesive materials.
(1) Japanese Patent Publication No. 51-8653 PA0 (2) Japanese Patent Publication No. 58-13116 PA0 (3) Japanese Patent Publication No. 63-41585 PA0 (1) With respect to Japanese Patent Publication Nos. 51-8653 and 63-41585: PA0 (2) With respect to Japanese Patent Publication No. 51-8653: PA0 (3) With respect to Japanese Patent Publication No. 58-13116:
A gas or liquid incompatible with an adhesive material being used is dispersed in the form of minute bubbles or drops within a solution containing the adhesive material. The adhesive solution so obtained (hereinafter, "adhesive solution" is referred to as a solution containing an adhesive material) is then coated onto release paper, forming a layer of the adhesive solution. Next, this layer of adhesive solution is heated, thereby forming an adhesive layer and also bursting the gas bubbles or liquid drops so as to form communicating pores.
A solution of an adhesive material in an organic solvent which can be extracted with an aqueous extractant is coated onto a porous backing, forming a layer of adhesive solution. This backing with the layer of adhesive solution is then immersed in the extractant, thereby extracting the organic solvent into the said extractant, and at the same time coagulating the said layer of adhesive solution. The replacement of the organic solvent by the extractant results in the formation of numerous communicating pores in the adhesive layer.
An adhesive solution is prepared by uniformly dispersing water or a mixture of water and a water-absorptive macromolecular substance in an adhesive solution containing a pressure sensitive adhesive material and an organic solvent. This adhesive solution is coated onto the surface of a sheet with adequate surface releasing properties, thus forming a layer of adhesive solution, which is then dried, and an air-permeable backing is then layered on this adhesive layer.
In this process, when the layer of adhesive solution containing the dispersed water is dried, the organic solvent is first evaporated to form an adhesive layer, and then the water is evaporated, thus forming pores where water was present.
However, the existing methods described above possess the following shortcomings.
In the processes comprising these existing techniques, an adhesive solution containing a uniformly dispersed gas or liquid incompatible with the adhesive material is used. However, a porous air-permeable tape with uniformly dispersed communicating pores cannot be obtained unless the uniform state of dispersion of the gas bubbles or liquid drops within the adhesive solution is adequately maintained.
Consequently, these processes entail difficult problems with respect to the preparation of the adhesive solution and control of the state of dispersion of the gas bubbles or liquid drops.
The previously existing technique described above suffers from the disadvantage that if, for example, the adhesive solution is coated onto the release sheet with a roll coater, then the water dispersed within the adhesive solution oozes from the layer of the solution by the pressure of the roller. Therefore, the method used for coating the adhesive solution onto the substrate is restricted.
Furthermore, since the water is dispersed within the adhesive solution in the form of drops with an extremely small diameter, when the layer of the adhesive solution is dried, the water is prone to evaporate together with the solvent. Consequently the formation of the desired communicating pores in the adhesive layer is difficult.
According to this previously existing technique, the use of the aforesaid adhesive solution is unnecessary. However, this technique does not permit the preparation of a tape with desirable air permeability.